1. Technical Field
This invention relates generally to radioactive gas removal, and in particular to removal of gas emitted during processing of radioactive material.
2. Prior Art
Storage and disposal of nuclear waste and contaminated material generated by the nuclear industry has always been a significant problem. Presently today there exists a substantial quantity of untreated radioactive waste material held in inadequate, substandard or temporary storage facilities. In particular, the enrichment process for nuclear fuels, primarily uranium, generates a substantial amount of waste material which, in the industry, is oftentimes stored at the bottom of specially designed water tanks. In the industry, this material is usually called an uranium raffinate and is a mixture of a large number of various radioactive elements suspended within, or agglomerated within water. The present preferred method of permanent storage for these waste materials is to somehow remove the waste materials from water storage and mix them in with other materials such as cement to form solid blocks which are then contained within the leak-proof permanent storage containers and which can be held and safely stored for the literally thousands of years necessary for the decay process to reduce the material to a harmless non-radioactive waste product.
The problem is that these waste materials, particularly uranium raffinate, contains entrained radioactive gasses, particularly radon gas which is a radioactive daughter product of radium 226, which itself is a decay product of uranium. As the uranium raffinate is being handled, for example, being removed from a water storage tank for eventual processing into solid form, some of the entrained radon will be released to atmosphere.
The present invention is directed to a pressurized radioactive gas treatment system for containing radioactive gas released from uranium raffinate and various other materials. The actual mechanical systems by which uranium raffinate or any other radioactive waste material is treated plays no part in the present invention. However, it is helpful to describe a typical system so as to put the present invention in a proper context so as to more fully appreciate this invention. It should be clearly understood that the following description is not intended to limit the scope of the invention, but is only intended to provide an aid in understanding it.
Uranium raffinate typically settles to the bottom of a water tank forming a semi-solid having a very high water content. This material can be dug, augured, scooped or shoveled out by mechanical means and when it is so handled, it turns back into a raffinate slurry, which is capable of being pumped. The raffinate slurry is then pumped into a holding tank which serves as a steady source of supply for additional machinery in further processing steps. These additional steps would include removing or reducing the water content from the raffinate, and then mixing the raffinate with other materials such as sand and cement to form solid blocks which can be safely handled and stored.
During this processing, each time the raffinate is disturbed, minute amounts of highly radioactive radon gas are released from the raffinate. These are found to be very small quantities on the order of just a few cubic millimeters per ton of material, but it is highly radioactive and cannot be released into the atmosphere. If it is, it can cause significant problems, particularly since radon is a gas and disperses well within the atmosphere and its decay chain includes significant particulate radioactive radon daughters of polonium, lead and bismuth.
Not only is there a problem of containing this released radon, there is also the problem of handling it since the quantities being released, although highly radioactive, are very small and difficult to handle.
For this reason, the storage tanks used in the initial stages of radioactive material processing, should not be vented to the atmosphere. However, this in itself is a problem, since current technologies in use today result in a de facto batch feed process for filling the tank and a continuous process for emptying the storage tank. For example, raffinate may be extracted from the water tank only during daylight hours, yet the outflow from the storage tank may be into a continuous process, which runs 24 hours a day. Thus, the amount of radioactive material stored within a storage tank may vary considerably during the cycle of operation, thereby making the use of an unvented tank unfeasible.
Accordingly, it is an object of the present invention to provide a system for collecting and safely disposing of quantities of radioactive gasses released from other radioactive materials during processing.